The present invention relates to a method of multistage gas phase polymerization using at least two fluid bed reactors in series, wherein the amount of subcomponents mixed in the polymer powder is reduced when polymer powder produced in an upstream arranged fluid bed reactor is taken up and introduced into a downstream arranged fluid bed reactor.
Furthermore, the present invention relates to a device for reducing the entrainment of subcomponents in the polymer powder as required in the implementation of the above method and relates to an apparatus of multistage gas phase polymerization including this device.
In the production of, for example, an ethylene/xcex1-olefin copolymer, it is common practice to employ a gas phase polymerization method in which a gas phase polymerization of a mixture comprising ethylene and an xcex1-olefin is carried out in a fluid bed reactor in the presence of a titanium based solid catalyst.
In the above polymer production, the use of a single fluid bed reactor results in the formation of a polymer whose properties necessarily fall in certain limited ranges. However, products of complex properties are increasingly desired in accordance with the diversification of market demands. Therefore, polymers of the same species but with varied properties, namely differing in molecular weight, purity and physical properties, have been produced by the employment of the method of preparing polymers with varied properties with the use of a plurality of fluid bed reactors connected to each other.
With respect to this method, a method of multistage gas phase polymerization, for example, a method using a two-stage gas phase polymerization apparatus comprising first fluid bed reactor 111, and continuously connected thereto, second fluid bed reactor 121 as shown in FIG. 3 is now widely employed.
Specifically, solid catalyst A is fed through supply line 115 into first fluid bed reactor 111. Simultaneously, a feed gas mixture consisting of, for example, ethylene and an xcex1-olefin is fed through supply line 112 into the first fluid bed reactor 111 at its bottom with the use of blower 113.
Hydrogen gas as a reaction inhibitor is premixed with the feed gas mixture in order to suppress the excess advance of the polymerization reaction. The molecular weight of the polymer produced by the first fluid bed reactor 111 as the first-stage polymerizer can be limited by appropriately terminating the polymerization reaction by the premixed hydrogen gas.
The fed gaseous olefin is passed through dispersion grid 117 containing, for example, a porous plate, which is arranged in the vicinity of the bottom of the first fluid bed reactor 111, and forms fluid bed 118 and maintains the fluid bed 118 in fluid form. Polymerization reaction is carried out in the fluid bed 118.
The thus produced polymer powder (particles) is continuously taken up, delivered into carrying line 125 by means of rotary valve 135 provided on take-up line 130, and fed through the carrying line 125 into second fluid bed reactor 121.
Unreacted feed gas having passed through the fluid bed 118 has its flow rate reduced in slowdown zone 119 provided in an upper part of the first fluid bed reactor 111 and discharged outside the first fluid bed reactor 111 through a gas outlet provided at the top of the first fluid bed reactor 111.
The unreacted feed gas having been discharged from the first fluid bed reactor 111 is passed through circulating line 116, is cooled by means of heat exchanger (cooler) 114 and joins the supply line 112. Thus, once more, the unreacted feed gas is continuously fed into the fluid bed 118 formed in the first fluid bed reactor 111 with the use of the blower 113.
On the other hand, the polymer powder taken up through the take-up line 130 from the first fluid bed reactor 111 is fed through the carrying line 125 into the second fluid bed reactor 121. Simultaneously, different feed gas mixture from that of the first reactor 111 is supplied through supply line 122 and through the carrying line 125 into the second fluid bed reactor 121 with the use of blower 123. Thus, fluid bed 128 is formed by the polymer powder, olefin gas and solid catalyst contained in the polymer powder in the second fluid bed reactor 121, and polymerization reaction is carried out in the fluid bed 128. Copolymer produced by the second fluid bed reactor 121 is continuously taken up through line 126.
The carrying line 125 is branched from the supply line 122, and a remote end of the carrying line 125 is connected to an upper part of the second fluid bed reactor 121. The olefin containing gas fed from the supply line 122 has its pressure increased by pressure increasing means such as centrifugal blower 141 and entrains the polymer powder taken up from the first fluid bed reactor 111 so that the polymer powder is carried and introduced into the second fluid bed reactor 121.
Although the above described the two-stage fluid bed reactor, namely the construction consisting of the first fluid bed reactor 111 and, continuously connected thereto, the second fluid bed reactor 121, use can also be made of a multistage fluid bed reactor consisting of a greater number of fluid bed reactors continuously connected to one another.
When a plurality of properties are imparted to the obtained polymer in the above multistage gas phase polymerization method, a feed gas mixture of desired composition is polymerized in an upstream fluid bed reactor, for example, the first fluid bed reactor 111, and the thus obtained polymer powder is taken up through the line 130 and fed into a downstream fluid fed reactor, for example, the second fluid bed reactor 121 so that the polymer powder is further polymerized.
In the second fluid bed reactor 121, the polymerization is generally performed with the use of a feed gas mixture of composition different from that of the upstream in the content of xcex1-olefin gas and hydrogen gas.
However, this method has a drawback in that, while desired property can be imparted to the polymer in the first-stage polymerization reaction, desired property cannot be imparted to the upstream obtained polymer in the downstream performed polymerization reaction.
The inventors have conducted extensive and intensive investigations of the cause thereof. As a result, they have found that desired property can be imparted to the polymer in the downstream polymerization as well by reducing the amount of xcex1-olefin and hydrogen gas (subcomponents) introduced together with the polymer powder to thereby regulate the composition of downstream supplied feed gas mixture during the transfer of the polymer powder from the upstream fluid bed reactor into the downstream fluid bed reactor. The present invention has been completed on the basis of this finding.
Under these circumstances, it is an object of the present invention to provide a method of multistage gas phase polymerization in which, when the polymer powder taken up from an upstream fluid bed reactor is carried while being entrained by a feed gas for a downstream fluid bed reactor so that the polymer powder is introduced into the downstream fluid bed reactor, hydrogen gas and comonomers which inhibit the polymerization reaction in the downstream fluid bed reactor and which render regulation of desired polymer properties difficult are removed from the polymer powder.
It is another object of the present invention to provide a device for removing subcomponents such as hydrogen gas and comonomers from the polymer powder taken up from an upstream fluid bed reactor before the introduction thereof into a downstream fluid bed reactor to thereby lower the subcomponent content of the polymer powder in a multistage gas phase polymerization apparatus. It is a further object of the present invention to provide an apparatus of multistage gas phase polymerization including this device.
The present invention has been made with a view toward solving the above problems of the prior art and attaining the above object. In one aspect of the present invention, there is provided a method of multistage gas phase polymerization, comprising performing polymerization of a feed gas mixture at least containing ethylene gas, an xcex1-olefin gas and hydrogen gas in an upstream arranged fluid bed reactor to thereby obtain polymer powder, taking up the polymer powder therefrom and performing further polymerization of the polymer powder in a downstream arranged fluid bed reactor, the downstream arranged fluid bed reactor continuously connected to the upstream arranged fluid bed reactor so that the polymer powder taken up from the upstream arranged fluid bed reactor is introduced into the downstream arranged fluid bed reactor,
which method comprises the steps of:
taking up polymer powder from an upstream arranged fluid bed reactor,
treating the taken up polymer powder so as to lower a content of xcex1-olefin gas and hydrogen gas therein, and
introducing the treated polymer powder into a downstream arranged fluid bed reactor.
The composition of feed gas mixture brought into actual reaction in each of the upstream and downstream arranged fluid bed reactors can be regulated in the above multistage gas phase polymerization wherein polymerization of a feed gas mixture at least containing ethylene gas, an xcex1-olefin gas and hydrogen gas is performed in an upstream arranged fluid bed reactor to thereby obtain polymer powder, the polymer powder is taken up therefrom, the content of unreacted xcex1-olefin gas and hydrogen gas in the polymer powder is lowered and the polymer powder is introduced into a downstream arranged fluid bed reactor. This enables changing properties imparted to the polymer in each of the upstream and downstream arranged fluid bed reactors in conformity with the use of the resultant polymer.
In the multistage gas phase polymerization method of the present invention, it is preferred that the above treating step be one in which a stream of given gas is introduced into the polymer powder taken up from the upstream arranged fluid bed reactor so that the xcex1-olefin gas and hydrogen gas mixed in the polymer powder are removed.
The subcomponent content of the polymer powder can be effectively lowered by removing subcomponents such as the xcex1-olefin gas and hydrogen gas mixed in the upstream obtained polymer before the transfer to the downstream fluid bed reactor.
In another aspect of the present invention, there is provided an apparatus for multistage gas phase polymerization, comprising:
a plural-stage fluid bed reactor, in at least most upstream of which a solid catalyst for polymerization is fed into a fluid bed reactor, and in each of which a feed gas mixture is blown through a dispersion grid into the fluid bed reactor from a bottom of the fluid bed reactor, to thereby form a fluid bed in the fluid bed reactor, and a gas phase polymerization reaction is carried out in the fluid bed so that a polymer is produced;
a carrying path branched from an introduction path for introducing a feed gas mixture into a downstream arranged fluid bed reactor and connected to an upper part of the downstream arranged fluid bed reactor; and
a line connected at its one end to the carrying path and connected at its other end to an upstream arranged fluid bed reactor,
wherein:
the feed gas mixture at least contains ethylene gas, an xcex1-olefin gas and hydrogen gas; and
in the carrying path polymer powder produced in the upstream arranged fluid bed reactor is taken up and treated so as to lower a content of xcex1-olefin gas and hydrogen gas (hereinafter also referred to as xe2x80x9csubcomponentsxe2x80x9d) in the taken up polymer powder, the treated polymer powder is introduced into the downstream arranged fluid bed reactor.
The composition of feed gas mixture brought into actual reaction in each of the upstream and downstream arranged fluid bed reactors can be regulated in the above multistage gas phase polymerization wherein polymerization of a feed gas mixture at least containing ethylene gas, an xcex1-olefin gas and hydrogen gas is performed in an upstream arranged fluid bed reactor to thereby obtain polymer powder, the polymer powder is taken up therefrom, the content of unreacted xcex1-olefin gas and hydrogen gas in the polymer powder is lowered and the polymer powder is introduced into a downstream arranged fluid bed reactor. This enables changing properties imparted to the polymer in each of the upstream and downstream arranged fluid bed reactors in conformity with the use of the resultant polymer.
In the multistage gas phase polymerization apparatus of the present invention, the above line is preferably fitted with separating means for removing the xcex1-olefin gas and hydrogen gas mixed in the polymer powder from the polymer powder.
Further, it is preferred that the separating means comprise a residence tank for temporarily retaining the polymer powder, an introduction passage for introducing a stream of given gas into the residence tank and a discharge passage for discharging the subcomponents,
so that the subcomponents mixed in the polymer powder retained in the residence tank are removed through the discharge passage by the use of the stream introduced through the introduction passage.
The subcomponents can be effectively separated from the polymer powder and removed through the discharge passage by arranging separating means comprising, for example, the residence tank, introduction passage and discharge passage, and temporarily retaining the upstream obtained polymer powder in the residence tank and introducing a stream of given gas into the residence tank through the introduction passage to thereby carry out purging. This enables effectively lowering the subcomponent content of the downstream fed polymer powder.
In a further aspect of the present invention, there is provided a device for reducing entrainment of subcomponents by downstream introduced polymer powder in an apparatus for multistage gas phase polymerization, the apparatus comprising:
a plural-stage fluid bed reactor, in at least most upstream of which a solid catalyst for polymerization is fed into a fluid bed reactor, and in each of which a feed gas mixture at least containing ethylene gas, an xcex1-olefin gas and hydrogen gas is blown through a dispersion grid into the fluid bed reactor from a bottom of the fluid bed reactor, to thereby form a fluid bed in the fluid bed reactor, and a gas phase polymerization reaction is carried out in the fluid bed so that a polymer is produced;
a carrying path branched from an introduction path for introducing a feed gas mixture into a downstream arranged fluid bed reactor and connected to an upper part of the downstream arranged fluid bed reactor; and
a line connected at its one end to the carrying path and connected at its other end to an upstream arranged fluid bed reactor,
the downstream arranged fluid bed reactor being continuously connected to the upstream arranged fluid bed reactor so that the polymer powder produced in the upstream arranged fluid bed reactor is taken up through the line and introduced into the downstream arranged fluid bed reactor,
which device comprises a residence tank for temporarily retaining the polymer powder, an introduction passage for introducing a stream of given gas into the residence tank and a discharge passage for discharging subcomponents,
so that xcex1-olefin gas and hydrogen gas (subcomponents) mixed in the polymer powder retained in the residence tank are removed through the discharge passage by the use of the stream introduced through the introduction passage.
The subcomponents can be effectively separated from the polymer powder and removed through the discharge passage by, in the multistage gas phase polymerization apparatus, temporarily retaining the upstream obtained polymer powder in the residence tank and introducing a stream of given gas into the residence tank through the introduction passage to thereby carry out purging. This enables effectively lowering the subcomponent content of the downstream fed polymer powder.